Svetlana Bashkova

The effects of urea modification and heat treatment on the process of NO2 removal by wood-based activated carbon

The removal of NO(2) on urea-modified and heat-treated wood-based activated carbons was studied. From the obtained results it was found that these modifications, especially when done at 950 degrees C, have a positive effect on NO(2) adsorption and on the retention of NO (the product of NO(2) reduction by carbon). The presence of moisture in the system enhances the removal of NO(2) but negatively affects the retention of NO. It is possible that the formation of active centers on the carbon surface and some increase in the volume of supermicropores during the high temperature treatment play a significant role in these removal processes. The surface of the carbons was analyzed in terms of the pK(a) distributions. The qualitative and quantitative analyses of the NO(2) adsorption products were carried out by means of FTIR and TA techniques, respectively. The main products found on the carbon surface were the NO(3) and NO(2) species.

Interactions of NO2 and NO with Carbonaceous Adsorbents Containing Silver Nanoparticles

Interactions of NO(2) and NO (the product of NO(2) reduction by carbon) with biomass-based carbonaceous materials with silver nanoparticles deposited on the surface were studied. The surface of the materials was characterized using adsorption of nitrogen, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The results showed that the amount of NO(2) adsorbed, its conversion to NO, and the amount of NO released from the carbon surface depend on the carbons content of silver. More silver results in a better performance of the adsorbent. The products of NO(2) interactions with silver include surface chelates such as Ag(2)-O-NO or Ag-O(2)-NO. Another element, active in the surface reactions with NO(2), is phosphorus. Both silver and phosphorus species are oxidized by NO(2). The product of NO(2) reduction, NO, is either retained on the carbon surface by its interactions with metallic silver or is further reduced to N(2)O or N(2). Besides silver, carbon support is also active in the reduction of NO(2) to NO. Carbon monoxide formed in such a processes can reduce silver oxide nanoparticles, and thus, it provides more metallic silver for interactions with NO.

Effect of surface chemical and structural heterogeneity of copper-based MOF/graphite oxide composites on the adsorption of ammonia

Two graphite oxides (GOs), obtained by oxidation of graphites of different origins, were used as composite components with copper-based metal-organic frameworks, MOFs. Such composites were tested for ammonia adsorption at room temperature, in dry and moist conditions. The materials were characterized by X-ray diffraction, FT-IR spectroscopy, adsorption of nitrogen, and thermal analysis. Generally, the ammonia adsorption capacities of the composites were found to be lower than those calculated for the physical mixture of their components. An involvement of NH3 adsorption sites of MOF in a composite formation was found to be a major factor, lowering the adsorption capacity of a composite in dry conditions. The composites with the smaller amount of GO were found to be better adsorbents of ammonia in the absence of moisture than those, with the higher amount of GO. The adsorption of ammonia in moist conditions resulted in a collapse of MOF structure, accompanied by the release of active groups. These groups contributed to the enhanced adsorption of ammonia via acid-base reactions. Thus, in the presence of moisture, the composites with the higher amounts of GO, and the ones, containing more carboxylic groups than epoxy groups in GO, were found to be the best performing samples.

Effect of silver nanoparticles deposited on micro/mesoporous activated carbons on retention of NOx at room temperature

Wood-based activated carbon was modified by deposition of silver using Tollens method. Adsorbents with various contents of silver were used to study NO(2) and NO (the product of NO(2) reduction by carbon) retention. The surface of the initial and exhausted materials was characterized using adsorption of nitrogen, XRD, SEM/EDX, FTIR and TA. The results indicated that with an increasing content of silver on the surface the capacities to retain NO(2) and NO increase until the plateau is reached. The performance depends on the dispersion of nanoparticles and their chemistry. Highly dispersed small silver metal particles promote formation of chelates with NO(2) and/or with NO. An excess of Tollens reagent results in formation of larger silver crystals and silver oxide nanoparticles. If sufficiently dispersed, they also enhance the retention of NO(2) via formation of nitrates deposited in the pore system. The surface of the carbon matrix is also active in NO(2) retention, providing the small pores and edges of graphene layers, where the reductions of NO(2)/oxidation of carbon take place.

Reactive Adsorption of NO2 at Ambient Conditions on Iron-Containing Polymer-Based Porous Carbons

Adsorption of NO(2) and retention of NO (the product of NO(2) reduction by carbon) on iron-containing materials prepared from polystyrenesulfonic acid-co-maleic acid iron salt were studied. The surface of the materials was characterized using nitrogen adsorption, XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and FTIR spectroscopy, and thermogravimetric analysis (TGA). The results showed the positive effects of the pore volume and well-dispersed iron species (Fe(2)O(3), FeSO(4), and FeS) on the performance of carbons as NO(2) adsorbents at room temperature. The retention of NO(2) on the carbon surface takes place either through its reduction to NO by carbon and/or by Fe(2)O(3), FeSO(4), and FeS, or through its reaction with Fe(2)O(3) and/or Fe(OH)(3), leading to the formation of Fe(NO(3))(3). The retention of NO is enhanced on carbons containing iron in the form of α-FeOOH, α-Fe(2)O(3), or γ-FeOOH. The best performance was found on the carbon with α-Fe(2)O(3). Dispersion and the particle size of iron compounds on the carbon surface affect both the adsorption/reduction process of NO(2) and the retention process of NO.